How to fix “Firefox is already running” error

Sometimes when you try to start Firefox, it warns you that Firefox is already running. The message looks like this:

Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.

Usually, you can just kill the firefox process to solve this problem. For example, on Linux the command “ps auxwww | grep firefox” will find the process number and then “kill [processnumber]” will work fine. But sometimes things are more horked than usual. That happened to me today, surprise surprise ๐Ÿ™‚ Here’s how to fix the deeper problem:

Step 1. Find your profile. This page tells you how to find the location of your Firefox profile. Under Linux (e.g. Ubuntu), it will be at ~/.mozilla/firefox/[Profile name]/ .

Step 2. Remove the lock files. This page tells you what the lock files are for Firefox on Windows/Linux/Mac. Under Unix/Linux, you’ll need to remove two files “lock” and “.parentlock” .

I haven’t had this happen before today, but it can happen if (for example) someone turns your computer off while Firefox is running.

78 Responses to How to fix “Firefox is already running” error (Leave a comment)

  1. Strangely enough my computer froze yesterday when i was browsing in Firefox – had to manually reset. Today when i started the browser it knew what happened and asked me if i wanted to restore the session (no error..).

    However, i got the error described in this post some time ago when i tried to launch Firefox. You know when you launch something and it sometimes takes (longer than expected) time to actually start (although you can see the process in Task Manager) ? Dunno why that happens, but that time when i launched Firefox it was the same. Didn’t know what happened in the beginning, so i launched it again. That’s when i got the error.

  2. Matt, you are lucky you got this for first time ๐Ÿ˜€
    This always happens to me – the resolution is far more simple in windows – ctrl+alt+del – then locate and “end” ‘firefox.exe’ process ๐Ÿ˜‰

    Worse situation is when you lost all your bookmarks and buttons – you have to go to your profile, location something like this:
    C:Documents and Settings%UserName%Application DataMozillaFirefoxProfilesdasc0fxi.defaultbookmarkbackups

    in bookmarkbackups are – guess what? – backups of your bookmarks ๐Ÿ˜‰

    Copy your most recent version in C:Documents and Settings%UserName%Application DataMozillaFirefoxProfilesdasc0fxi.default and rename it to bookmarks.html (first remove the older file)
    That’s to restore the bookmarks ๐Ÿ™‚
    For the buttons – simply delete “localstore.rdf”, located in C:Documents and Settings%UserName%Application DataMozillaFirefoxProfilesdasc0fxi.default

    Hope this was useful ๐Ÿ™‚

  3. Nunya B Usiness

    This happens to me when I goof the sharing of firefox bookmarks via a share drive and common profile file. I dual boot an XP and FC5 machine with my users have their mozilla profiles on a share. If I use the wrong filename (misread letter l for the number 1 for instance) I get the error message.

  4. Partially Behind Dave

    It is quite annoying huh Matt, good stuff…I wonder how many people just restart.

  5. Just got a copy of Ubuntu in the mail, for those who want to try it go >

    Thanks for the tips!

  6. firefox is a great browser, the problem is that it is starting to behave more and more like his un-official brother…..
    there are 3 main issues that i got with FF:
    1-memory cosnumer…
    2-Slow activation-my winxp is restarting daily…
    3-images on websites not looking so good.

    great blog!.

  7. I get that firefox message many days a week. I consider it a major bug: not only should ffox fix its own corruption, but it should not be able to get into (or even near) that state.

    Obviously the web browser is going to be the main program we run on our computers. Yet if I said I wanted my IM tool, my word processor, my web page viewer, my shell, and my MUA to be all in one big process with one shared memory space, unable to be run simultaneously on multiple boxes (with shared home dir), people would accuse me of throwing out 20 years of OS development.

    The ffox folks probably say they’ve “optimized for the common case” or they’re “making things convenient for their users by locking all the profile settings to one process”. I don’t get it, though. I can share my volatile imap inbox across multiple processes (on multiple boxes), but my barely-changing set of trusted SSL certs is too difficult to share between two long-running web browser processes?

  8. I’ve been using Linux for a while but not too familiar with all the linux commands – I prefer the GUI so I go to the System Administration tab in my menu, then system monitor – you can easily find and kill any bad processes here.

    I find I do this with Firefox a lot but also media players – VLC seems to be the worst for this – you can run multiple instances but it starts to bog the system down when you get 2 or 3 going at once (that is 2 that didn’t properly close in the first place plus the one you are currently using).

    This method works (as far as I know) on Fedora, Debian and Ubuntu as I run all 3 of these at home.

  9. We actually wrote a custom script for our Linux desktop users that would check for and remove the lock files *every time* they started Firefox. A quick and dirty workaround, no doubt, but having ten end-users complaining about this problem multiple times per week got to be unbearable.

    I will say that Firefox 2.0 seems to be a bit better about this problem though.

  10. I’ve had the same problem here on some networked iMacs. I ended up writing a script to fix it and then I used Platypus to make it a clickable app.
    This is for Mac OS X. Adjust the paths as necessary. (As you can see from the “Phoenix” line I’ve been using it a while.


    ### Remove the Mozilla Lockfile
    find ~/Library/Mozilla/Profiles -name .parentlock -exec rm {} ;

    ### Remove the FireFox Lockfile
    find ~/Library/Phoenix/Profiles -name .parentlock -exec rm {} ;

    ### Remove the FireFox Lockfile from the NEW location
    find ~/Library/Application Support/Firefox/Profiles -name .parentlock -exec rm {} ;

  11. You can receive that message if your operating system allows more than one user connected at the same time (Windows 2003 for example).

    If you’re logged in on the PC, using Firefox and you connect from another computer to your computer and log in using the same account, when trying to start Firefox you’ll get that message because the lock files exist but the Firefox in the remote connection can not access the Firefox from the other session.

    I’ve actually reported this “bug” a few months ago to the team and i got stupid answers, the conclusion was that they won’t bother to fix this. (didn’t argue further, it was pointless)

    They also mentioned a possible workaround, here’s the bug listing and the workaround:

  12. I do’t personally use Firefox frequently, but am a bit of an experienced *nix admin.

    Is there any easy way to tell Firefox to store it’s lock files somewhere else? Specifically, in /tmp or your OS’s equivalent, designed for such things and typically cleared out by the OS when the system is started, thus avoiding the computer-shut-down-with-firefox-open-and-left-the-lock-files-behind issue completely?

  13. Firefox was great at first however I feel personal that browser wise Firefox is slipping and others have caught up. I’ve gone back to IE and the new browser is great, you’ve pointed out one problem with firefox but I feel there is a lot more wrong.

  14. I’ve encountered this problem many times in the past, not since I upgraded to 2.0. I love firefox and the thousands of extensions that are available for it

  15. First of all: IE is NO alternative for dual boot systems ๐Ÿ˜‰

    if you follow this instructions, you might experience the problems described above.
    We could fix the problem with plain symbolic link instead of regular path.

    Works great.

  16. Thanks for the great post. This happens to me way too much in Firefox. The fix is a lifesaver!

  17. I only get that problem because I like to run multiple Firefox profiles (at once or not) and I had to modify the shortcuts to look something like this:

    D:Program FilesMozilla Firefoxfirefox.exe” -p profilename -no-remote

    This problem pops up when Firefox is running and an external application tries to open a new Firefox window (for example, from help file, or pdf file or whatever). I still haven’t found a way to solve this ๐Ÿ™

  18. ON windows XP:
    Just go to C:Documents and Settings%Username%Application DataMozilla and delete all…

  19. Andrew,

    YOU WROTE: “This problem pops up when Firefox is running and an external application tries to open a new Firefox window (for example, from help file, or pdf file or whatever). I still havenโ€™t found a way to solve this.”

    SOLUTION: Right-click on “My Computer”, then click “Properties” > “Advanced” (tab) > “Environment Variables”. Under “System variables”, delete the “MOZ_NO_REMOTE” variable.

    I had the same problem you described, and this solution worked for me. Hopefully it will work for you also!

  20. One can get the ‘Firefox is already running’ error message in another way too as it happened to me. There was no running firefox process and there were no lock files in the profile directory. The problem was that the profiles.ini file contained a defunct profile name like this:
    Name=Default User

    Because of the Default=1 line, firefox was trying to open the sz23zs32.default directory which didn’t, in fact, exist. Deleting the above lines from the profiles.ini got my firefox back up again.

  21. Thanks a lot, it worked !!

  22. Hi Matt

    killall will take a process name as opposed to a process id.

    killall firefox (when you really mean to, of course :P)

    It’s part of the psmisc package if you don’t have it installed by default.

  23. Elizabeth MCGuire

    I 8use mozilla fire fox. i keep getting error ads need to be loaded from adcode. what is the problem and how can i fix it. when visiting a website it keeps saying windows cannot find null.

  24. Unfortunately, none of this hasn’t worked for me. I have no lock files, I have Administrator rights, and I’ve even reinstalled FireFox to no avail. Avast hasn’t found any viruses but something is deadly wrong. After I reinstalled FireFox still had 2 profiles I had created beforehand. Can anyone help? My IE isn’t saving cookies and Safari is not ready for prime time.

  25. Been wanting to use firefox for a weeknow and it didnt work. renaming the profile sure did the trick. Thank you.

  26. we use firefox on windows XP because it’s much faster than IE, but yesterday we downloaded themes for our firefox and just so happened that our firefox started to display “Connection Reset” and we can no longer use the browser. And even if we uninstalled our existing firefox, and installed a new one(same version and other versions), it still produces the same result. Does it has anything to do with the themes? how can we fix this problem? we definitely want to use firefox again! please help, thanks.

  27. Daniel: I have the same problem Andrew has, but I don’t have a MOZ_NO_REMOTE environment variable set anywhere. Like Andrew, I’m using the -no-remote command-line switch, not an environment variable, in order to run multiple instances.

    This problem occurs even if I have only one instance running, so long as that instance is not using my default profile.

    My GUESS is that when you click on a link, it wants to activate your default profile. If I only have one copy of firefox running, and it’s using my default profile, then clicking on the link will work. If I have two copies running, then clicking on the link won’t work. If I have only one copy running, but it’s NOT using my default profile, then clicking on the link won’t work. Sometimes it’s annoying and cumbersome to get the URL to copy-and-paste it: e.g., if you get an email with a link in it.

  28. What if I can’t delete the “parent.lock” file?
    Everytime I try, a window comes up saying “Cannot delete parent: The file or directed is corrupted and unreadable.”

  29. Hi Judy,

    If you’re using windows, you can try this program:

    Otherwise, if you’re using Linux, at a command prompt, type in:
    lsof ~/.mozilla/firefox/[Profile name]/.parentlock
    If nothing shows up there, you’ve got a much bigger problem. You’re going to have to umount the file system or mount it read only mode and run fsck (file system check) on it.

  30. Thanks Nevyn,

    I downloaded the Unlocker program, but it still didn’t delete the parent.lock file.
    And I have no clue what you mean by umounting the file system?

  31. If mozilla is displaying this because you are on a network with a roaming profile which happens alot you just go to C:Documents and Settings%Username%Application DataMozillaFirefox and modify the profiles configuration settings to another path, or remove completly and save, this should keep this from happening.

    Thanks Ron

  32. Justin, Daniel, Andrew: This might be a bit late but this is how I got around this same problem. I created two shortcuts to my Firefox (one for the default profile and one for my second). For the default profile I left the shortcut path at its default value (C:Program FilesMozilla Firefoxfirefox.exe) but for the second profile I added the -P and no-remote switches (C:Program FilesMozilla Firefoxfirefox.exe -P “Profile Name” -no-remote). While I had this problem I was using the -P “Default” -no-remote on my default shortcut (where I think the problem was)

  33. I have windows xp media center edition OS.

    Firefox says firefox is already running please close it to open a new.. blah blah blah you know the deal.

    Already tried going into task manager, not there so i cant end firefox.exe.

    I’ve reinstalled, i’ve restarted.

    Anything else i should try???

  34. i am having a error and i have been having for a while it says that fire fox is already started and i must close it the case is that is will not show up on my prosses can some one please help?

  35. Richard Barrington-Hill

    Hey all – to fix this problem I wrote a batch file (If you have windows folow this:)

    Open Notepad.
    Paste in the following :

    ———–Copy Below Here————-

    @echo off

    set exeName=%~1
    if “%~1″==”” set exeName=”firefox”
    if “%exeName%”==”” echo Processing aborted&pause&goto :EOF
    call :GETNAME “%exeName%”

    set found=

    for /f “tokens=*” %%a in (‘tasklist ^| findstr /i “%fileName%”‘) do set found=Y

    if “%found%”==”Y” call :endfirefox
    taskkill /f /im “cmd.exe”

    set fileName=%~nx1
    goto :EOF

    @echo off
    taskkill /f /im “firefox.exe”
    “C:Program FilesMozilla Firefoxfirefox.exe”
    taskkill /f /im “cmd.exe”

    ———–End above here————-

    Save as killfirefox.bat (it’s important it saves as a .bat and not a .txt).

    Place it on your desktop – if you get that error message simply run the batch file, and it’ll fix it AND start your browser for you.

    Nice ๐Ÿ˜›

  36. In Open suse
    Open —> Terminal Program …
    Type this command
    rm -rf .mozilla

  37. Had the same problem on FF3 on Vista.
    firefox.exe -profilemanager
    Selected “Create New”
    Pointed it at my old profile directory, select Next. Old settings rebuilt and all my settings came back.

  38. Hey, I just had this problem in XP, and went to the mozilla site to try to fix it. I followed all their directions, but wasn’t able to find a lock file like they mentioned.

    On a whim, I just went to the taskmanager and manually typed in “firefox.exe” as a new task to be run. It seems to be fine now. I exited and re-opened firefox with no prob, just to check. Hope this can work for some of you guys. Almost seems too easy…

  39. I’m late on this thread but I am trying to solve this problem, and using the advice in this thread. Wish me luck. ๐Ÿ™‚

    I’d like to link the list of add ons that are known to cause problems – I wonder if IE Tab was giving me trouble. I can’t install IE View Lite because I’m in the latest FF version (a Beta) because I needed a different add on that was only for the Beta (SIGH) ๐Ÿ™‚

    In case this helps anyone:

  40. On linux if all else fails I’ve found in the past:
    running in bash
    firefox -ProfileManager
    starts the profileManager for creating to create a new profile
    and then start everything up smoothly and even copy your
    old profile’s bookmarks into the new one, will also work in Windows I think
    for more information

  41. I dont know if anybody can help me but, I’ve been using firefox and ever since i upgraded to 3.05 i cannot get a connection to the internet and its been doing this for about a week

  42. Haha I’m a nub, I’ve just been restarting my PC manually for ages because I couldn’t be fucked looking up a solution. Took me all of 30 seconds to find this page (Ctrl+alt+del and ending process wasn’t working for me)

  43. I had the problem (frequently) with Vista.

    Rebooting always fixed it, but I’d had enough, and wanted to fix it without rebooting.

    I found the parent.lock file in C:Users\AppDataRoamingMozillaFirefoxProfiles, and tried to delete it. Windows prevents it, saying that it’s in use (even though Firefox is not in the task manager).

    So I opened up a DOS shell, cd’d to C:Program FilesMozilla Firefox and ran “firefox.exe -profilemanager”.

    I created a new profile, and used the browser (in the wizard) to make it point to the old profile. No dice – it still thinks the “parent.lock” is in use.

    This worked:

    – I used Explorer to copy the profile folder, within the Profiles folder. Windows doesn’t copy the “parent.lock”, and another file, because they are “in use”. Rename the new folder to “new.default”
    – Run “firefox.exe -profilemanager”
    – rename the old profile to “”
    – create a new profile, call it “default”
    – When the wizard asks for a profile folder, browse to the copied folder, ie. “new.default”
    – Run Firefox!

  44. Jonathan,

    Thanks, that circumvented the current problem on hand of mozilla not starting up.! I use fC 6 and the problem is resolved.


  45. I had the same problem, but had been running my main profile using the -no-remote switch. To be able to run links from external programs (e.g., double clicking a link in an email client), the -no-remote switch has to be removed. Mozilla’s documentation states that it should never be run for the default profile (which it would seem also applies to whatever profile you use most of the time). (This documentation was mentioned in the original article above and may be found here:

    For the record, I removed the switch and everything works like a charm now.

  46. as root copied the entire /root/.mozilla directory in over the .mozilla directory for the user w/ the issue. Updated permissions and ownership….all better

  47. I fixed firefox by uninstalling zone alarm and using comodo firewall

  48. why should i have to go throught all this stuff which I do not understand to use a browser that is supposed to be better than IE. I don’t have time for this crap. It makes me want to give in and just use the damn IE.

  49. I found that to bypass the error, not fix was to create a .bat file. It’s this exactly:

    taskkill /im firefox.exe
    START firefox.exe

    Since you usually close firefox manually you don’t need to worry about accidentally pressing the button. This just prevents the Firefox is still running by beating it to the finish line. First it ends the FireFox process, and then 2 Seconds later it starts firefox up.

  50. thnxxx

  51. I have 2 accounts on my PC. When I go to the other account I close Firefox on the one I’m leaving. The problem is when I go to the other account and open Firefox and try to update my Add-ons I keep getting the error message that, “The update could not be installed. Please make sure that there are no other copies of Firefox running on your computer, and than restart Firefox to try again.”

    I get the same error message when I try to update my Add-ons on my other account, too.
    This is a fairly new problem.

    Thank you, Patricia Rodela

  52. hello
    i get every time when i start firefox or msn i get a error
    i have installed again but its stay the same the error is :

    can entrypoint from procedure_except_handler4_common not find in dll-file msvcrt.dll

    i download allready a new .dll but not working.

    please can somebody help me.


  53. This problem of “Application already running, please close existing WHATEVER before running WHATEVER” ALTHOUGH it does not appear on your task-bar seems to be a frequent little glitch in Windows 7.

    The solution is VERY simple and applies to ALL applications. Run the application “Resource Monitor”, you will find this application in your “System Tools” file when you open your “All Programs” menu (the menu you get by simply putting your mouse on the bottom left corner).

    In Resource Monitor there is a tab called OVERVIEW (I believe it’s the tab that will first open anyway). Make sure you are in that tab, scroll down the applications until you find the one the computer is saying is still open, then “right click” and hit “end”.

    This will immediately solve that problem. I find this happens so much I have the Resource Monitor Icon on my Wallpaper screen.

    Hope this helps, I sure does for me.


  54. “How to fix โ€œFirefox is already runningโ€ error , January 2, 2007, in How to, Linux/Ubuntu”
    helped me fix the issue in 2 secs.. it is coz the server rebooted when i was running firefox, thus it have lock and .parentlock file inside..thanks a lot ๐Ÿ™‚

  55. After reinstalling and several other attempts I finally solved this problem by using the advice of Mathew’s August 31, 2007 post. I deleted the “Path=xxxxxx” line in the profile.ini file.

  56. I never experienced this problem before yesterday and it was frustrating that the mighty ‘killall’ was not working. Thank you so much Matt! ๐Ÿ™‚

  57. when i use mathews protocol from Aug 31 2007, firefox restarted with a new profile. But the old profile is completely gone and I lost al my bokmarks. I found a cache folder in local settings but the profile folder with bookmark backups is gone! is there any hope? anyone know what i am talking about?

  58. This is all well and fine if you have some knowledge of computers and where to find these files and fix them, but I don’t.

    Is there a dumbed down version of showing how (and most importantly) where I go to fix this error message.

    I have gotten the error message often enough, but this is the first time that a restart did not fix it…I am not sure if it matters, but I my computer was a bit slow loading pages every so often for the past couple of days.

    I would greatly appreciate any help! Thanks so much!

  59. Surely we have had enough ‘fixes’ for this problem, all of which assume that the user has made an error. This is very clearly a Firefox’ problem – I have even found it after a completely clean new install of Windows7 and no ‘other’ software or add-ons.
    What would be nice would be an acknowledgement from Mozilla that there is a problem. I have been a loyal user of Firefox since the very early days, but reluctantly I will now switch to the dreaded IE8 until thge FF issue is resolved… may be slower, but at least it doesn’t freeze every time I use it.

  60. My FFox does the same thing , after a number of various web sites , it keep running in
    the back ground …. CTRL ALT DEL , then end process works but Its getting to be a pain
    Im using a fresh Install of Windows XP PRO …. no virus … no malware …. thought Ffox
    would fix this or give us a work around , I dont want to go to IE8

  61. for non-admin users who are experiencing this same issue, here’s what I had to do to get it done…
    – Tried to end the firefox.exe process via “CTRL-ALT-DEL” but there was no firefox.exe running
    – Had to access Profile folder (%APPDATA%MozillaFirefoxProfiles) in an attempt to delete “parental.lock” but was unable to do so, so we had to run “Chkdsk”.
    – Since this specific user account is non-admin, I had to briefly change the user account to full admin so I can run “Chkdsk”.
    – Ran “Chkdsk” via My Computer (simply follow steps: — check “Automatically fix file system errors” check box, and then click Start.
    – once scan is done, reset pc.
    – let “Chkdsk” to its thing — you should see a list of errors or files that are going to be deleted.
    – wait for your pc to fully boot up again… test it… it should be back to norm.
    – once all is good, change user account back to non-admin.
    – done.

    Hope this helps those who may be having the same issues I had… cheers!

  62. rename/removing/moving the profiles.ini file did the trick specifically. Im running linux…. some flavor or FC.

  63. I am a long time user of Ubuntu and have followed the upgrade path to 10.04, but as far as I am aware there are no versions of Linux that are suitable for non-technical users. Every package has serious flaws which are seldom addressed promptly, if at all.

    And one can look in horror as new users are serially abused by Linux shell-backs who seem to worship the Terminal. Any time someone says, ‘Just open a terminal session and type…’ it means (in the real world) that this software is broken.

    If you are trying to use your PC for something you rely on- as opposed to playing at computing – then Linux is simply not there yet. And given the fractured nature of OpenSource development it probably never will be.

    Without a financial imperative there simply is not the incentive to go back and fix broken things. Irresponsible? No, it is simply much more fun as a Developer to work on new stuff – and hey, if you are working for free – why not?

    So welcome to the world of Linux. Good luck – you are going to need it.

  64. how do i get rid of this message and is it secure

    Although this page is encrypted, the information you have entered is to be sent over an unencrypted connection and could easily be read by a third party.

    Are you sure you want to continue sending this information.

    Continue or cancel

  65. this happens every time I close firefox and then want to open it again, must remember to always keep a firefox window open (though this is hard as this laptop is wont to freeze or ‘not respond’ whenever it gets the chance. The annoying thing is that it thinks firefox is still open when it isn’t, there is therefore no way I can close firefox…. even ctrl alt del wont work, as it isn’t running. The only way out is to restart :/

  66. I used to get that all the time and still do. If that happens Click START then RUN type explorer.exe in the command box, click OK and wait for the window to pop open, close the explorer window and then launch firefox again. I don’t know why it works, it just does.

  67. I have this problem on one of two profiles. TaskMgr doesn’t show the process running. can’t find the profiles by any means advised her in the forum. Uninstalled completely with Revo and Mozilla uninstaller. Still won’t run under wife’s profile. Using Win Vista32.

  68. Purushottam Samarai

    Nevyn February 11, 2008 at 4:14 am
    Hi Judy,

    If youโ€™re using windows, you can try this program:

    Otherwise, if youโ€™re using Linux, at a command prompt, type in:
    lsof ~/.mozilla/firefox/[Profile name]/.parentlock
    If nothing shows up there, youโ€™ve got a much bigger problem. Youโ€™re going to have to umount the file system or mount it read only mode and run fsck (file system check) on it.

    hey Nevin, I was frustrated with firefox behaving like this. But your suggestion of using UNLOCKER worked…’

    Many Many Thanks from the bottom of my Heart..

  69. I had a problem with Firefox, and was looking on lots of web pages for a solution but couldn’t find it, temporary solution is of course ctr+alt+delete and then kill the process. But it gets annoying when you have to do it every single time you wanna shut it.
    Today I found it!
    Its winamp add-on, just uninstall it, restart Firefox and problem solved for good!

    If you have winamp add-on, it will keep bugging you with message:”Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.”

  70. Wow, as I research this I see that people have been talking about it for YEARS, across multiple major revisions of Firefox, on multiple operating systems. What gives? I have this issue with Firefox 3.6 on Win7. Have tried changing permissions on profile files, I *am* running as admin, so it should be able to do it anyway, the fixes don’t work (permanently anyway). Yes, I can always use the task manager to fix the problem, but it’s really, really annoying to do this several times per day. Are they never going to fix this?

  71. yes, I still had this problem too, and I just add on the BEGINNING of the command line of Firefox
    rm /home/daniel/.mozilla/firefox/wqu081dr.default/.parentlock

    So I’m sure it is erased by default, and my firefox ๐Ÿ™‚

    The way I did it: right click on the icone of Firefox and change the execute line of firefox this way
    rm /home/daniel/.mozilla/firefox/wqu081dr.default/.parentlock & x-www-browser %U

    Have fun!

  72. Thanks for the how-to! This problem can also arise when you are tunneling Firefox through an ssh connection, and the connection is interrupted.

  73. The Winamp plugin does seem to have been the culprit, as Nikola pointed out. So far so good, hope its a permanent fix

  74. If you are facing the issue of running firefox in your linux machine please try running below command in your linux machine. It will work out.

    rm ~/.mozilla/firefox/*/.parentlock

  75. I’m having this issue using Selenium Remote Control and 13 firefox instances (The app I’m testing uses certifcates to handle user permissions/roles instead of usernames and passwords 13 Roles = 13 Firefox instances).

    I have no firefox processes showing up in my task manager and start the remote control (which starts firing off the 13 instances of firefox). Randomly, and not even 100% of the time, I get one of the profiles giving me the error – “Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.” when I know with 100% certainty that the profile in question isn’t being used.

    I’m wondering if there is some block of memory that isn’t being cleared on startup and periodically the block gets used by firefox and it “thinks” the profile is in use.

    Any one have ideas ?

  76. Today I’ve joined the club getting the message (in a small pop-up box) that firefox is already running. But it doesn’t appear on Task Manager. Rebooting doesn’t change it. I’ve tried the above suggested batch files and profile fiddling without success. Removing and reinstalling firefox looked promising, but once the browser was closed any attempt to re-open got that message again.
    So I can’t close firefox and I can’t open it. But I want my bookmarks, which as far I understand are in a ‘.json’ file. Being unable to open the firefox browser I can’t export them to another browser – yes, I agree, it’s a shame to think of using another browser when firefox has been my favourite for so long.
    Does anyone know if and how the .json file can be converted and/or the data extracted to enable the bookmarks to become ‘favourites’ or whatever a new browser demands?

  77. This is a bug of Firefox, but I think it is must not be the reason of not using it. On the whole, I think that Firefox is one of the best web browsers.

  78. Today is October 15 of 2014, and I am running version 24.2… and still have the same issue…it is annoying, but we have no choice – I can’t install IE on Linux yet…